ErrorSubmissionQuotaExceeded exception occurs in Microsoft Dynamics 365 mailbox

This article provides a solution for an "unknown error occurred while sending the email message" error that occurs in a Microsoft Dynamics 365 mailbox.

Applies to:   Microsoft Dynamics 365
Original KB number:   4486353

Symptoms

An email isn't sent from Dynamics 365 and you might see the following error message is logged in the Alerts area for a user's mailbox:

An unknown error occurred while sending the email message [Email Subject] through the mailbox [Mailbox Name]. The owner of the associated email server profile Microsoft Exchange Online has been notified. The system will try to send the message again later.
Email Server Error Code: Exchange server returned UnknownOutgoingEmailIntegrationError ErrorSubmissionQuotaExceeded exception.

Cause

The alert is logged because the message size exceeds Exchange Online quota limits. For example, 10,000 emails within 24 hours.

Resolution

To solve this issue, avoid exceeding the Exchange Online quota limits or use another email service that specializes in sending bulk email (for example, Dynamics 365 Customer Insights - Journeys.)

Note

Exchange Online customers who need to send legitimate bulk commercial email (for example, customer newsletters) should use third-party providers that specialize in these services.